The present invention is directed to a program-controlled communication system to which communication terminal equipment are connected that have line keys and/or function keys with whose actuations switching-oriented procedures and call setup procedures can be initiated. The information initiating and controlling these procedures as well as the key identification information is contained in memory areas of a database respectively allocated to a key which the central system control accesses. Device-related information including, among other thins, information about connection configurations, authorizations and services and information about physical functions such as, for example, the type of interface is stored within the database. At least one group composed of one first communication terminal equipment and one second communication terminal equipment is provided as such a device configuration and an incoming call addressed for the first communication terminal equipment is simultaneously signaled at both the first and second communication terminal equipment, preferably in different ways. Call-associated information can be weitten into and read out from memory sections of a main memory to be dynamically allocated and that serve as call register elements and as what are referred to as waiting list memory elements. The call-associated information is written thereinto and read out therefrom by the central system control both during the call setup as well as for an existing call.
A modern digital, computer-controlled communication switching system is fundamentally composed of a plurality of switching-oriented function units and of a programmable, digital computer system that controls the function units and monitors all switching-oriented operations. To this end, the computer system is informed with information about the operating status of the function units and about status changes, particularly about inputs at the connected terminal equipment. It can therefore immediately produce and output appropriate control instructions and messages as needed.
In addition to being capable of executing the actual switching control, such communication switching systems, particularly telephone private branch exchanges, are also capable of realizing a control or realization of additional control procedures that proceed beyond the actual switching event. Such additional functions are generally referred to as performance features, whereby a great number of different performance features is particularly known for the communication service of "voice". Such performance features can be initiated either when seizing the switching equipment or during a call that already exists. Included, for example, among such performance features are preventing undesired calls, acoustic and/or optical prompts portrayable on an optical display means for waiting subscribers and for the respective operator of a terminal equipment in different switching-oriented statuses, as well as the possibility of a consultation with another subscriber proceeding from an existing call. In such a case, the partner of the original call is switched into a waiting position, whereby this original call can be taken up again after a consultation call.
A special configuration can exist for a plurality of terminal equipment connected to the communication switching system insofar as a call that is intended for a specific terminal equipment of this group is simultaneously signaled at all other terminal equipment belonging to the group. It is accepted with priority at a terminal equipment intended for this purpose (multi-line appearance). For example, such terminal equipment can be allocated to an executive subscriber and to the secretary. Such terminal equipment having a special constellation with respect to one another can also belong to a group of terminal equipment that are equipped with functions as are usually standard for terminal equipment utilized in what are referred to as key telephone systems. This means that the switching-oriented seizure of subscriber lines, the setup of internal connections and the use of performance features occurs in response to key actuation. These functions are realized by programs integrated in the private branch exchange. The information exchange required for this purpose between the terminal equipment and the private branch exchange is possible on the basis of a subscriber signaling procedure in a signaling channel arranged between the system and the terminal equipment. The control of the optical displays that provide information about switching-oriented statuses of one's own terminal equipment and of the other terminal equipment of the group then also occurs on the basis of the signaling information transmitted thereover. All switching-oriented procedures for the terminal equipment of this group initiated by the line keys in the communication terminal equipment are realized in the communication system.
Given a call setup, a memory element of a dynamic memory is respectively allocated and identifiers that identify the terminal equipment participating in such a call are written into this memory element. When, for example, a plurality of such calls are chained in such a way that, for example, terminal equipment that are in a waiting position or in a current connection are to be identified in conjunction with a multiply undertaken consultation, then this requires a corresponding high number of entries in one and the same call register. Given more than three entries related to terminal equipment that, for example, can relate to the identifier for the two terminal equipment participating in a call and can relate to the identifier for a terminal equipment situated on hold, an increased outlay for computer capacity and, necessarily, an increase programming outlay for the control and administration procedures is required for forming the information related to terminal equipment that proceed beyond this and for administering this information. Among other things, these administration procedures have testing routines with which an identification must be made to determine if a status change has occurred in the relationship of the individual devices relative to one another or if a device has disconnected, for example by hanging up.